Organic light emitting device and display unit

ABSTRACT

An organic light emitting device capable of improving the light extraction characteristics while suppressing the driving voltage and improving the luminescent performance, and a display unit using it are provided. The organic light emitting device includes: a lamination structure that includes a cathode, a plurality of layers including a light emitting layer made of an organic material, and an anode including a metal thin film in this order, in which the cathode is reflective and the anode is semi-transparent to light generated in the light emitting layer; and a resonator structure that resonates the light generated in the light emitting layer between the cathode and the anode.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2006-208051 filed in the Japanese Patent Office on Jul.31, 2006, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light emitting device havinga light resonator structure and a display unit using the organic lightemitting device.

2. Description of the Related Art

In these years, as one of flat panel displays, an organic EL displaythat displays images by using the organic EL (Electro Luminescence)phenomenon has been noted. Since the organic EL display is aself-luminous type display that displays images by using the foregoinglight emitting phenomenon, the organic EL display is superior in termsof the wide view angle, the small power consumption, and the lightweight.

The organic EL device mounted on the organic EL display mainly has astructure in which an organic layer is provided between an anode and acathode. The organic layer includes a light emitting layer as a lightemitting source and a hole-transport layer, an electron transport layerand the like for emitting light from the light emitting layer.

Specially, in an active matrix drive system organic EL display unit, thetop emission structure capable of maintaining a large aperture ratio ofa pixel has been developed (for example, refer to Japanese UnexaminedPatent Application Publication Nos. 2003-203781, 2003-203783,2003-323987, 2004-146198, 2004-152542, 2005-032618, 2005-276542, and2005-530320). Such a structure is a device structure having alight-reflective lower cathode and a light-transparent upper anode, anddifferent from the structure having a light-transparent lower anode anda light-reflective upper cathode that has been developed in the past.The top emission structure is not affected by lowering of the apertureratio due to a TFT (Thin Film Transistor) and wiring. Therefore, it isthought that the top emission structure can provide an organic ELdisplay unit with high display performance and superior long-termreliability.

Further, in the top emission structure, as a technique to improve colorpurity of blue light, green light, and red light, the followingtechnique has been known. In such a technique, in the device structurehaving a light-reflective lower anode and a light-semi-transparent uppercathode, light generated from the light emitting layer in the organiclayer is reflected and resonated (for example, refer to InternationalPublication No. WO 01/039554 and Japanese Unexamined Patent ApplicationPublication No. 10-177896). The device structure of the organic ELdevice having the light resonant function is generally called “lightresonator structure (so-called micro-cavity structure).” In particular,in the organic EL device having the light resonator structure, the lightextraction efficiency is improved, that is, the front optical power isincreased, and the color purity is improved. Therefore, the organic ELdevice having the light resonator structure is suitable for a full colordisplay.

SUMMARY OF THE INVENTION

In these days, the practicality of the organic EL display has beenwidely recognized. Accordingly, improvement of the display performancethereof has been increasingly aspired. However, in the past, theluminescent performance of the organic EL device that affects thedisplay performance has not been sufficient yet, and has left much to beimproved.

For example, in the device structure in Japanese Unexamined PatentApplication Publication Nos. 2003-203781, 2003-203783, 2003-323987,2004-146198, 2004-152542, 2005-032618, 2005-276542, and 2005-530320, thetechnique is based on the premise that an upper anode with the highlight transmittance is used. The material of the upper anode is limitedto a metal oxide conductor. The metal oxide conductor is generallysputter-deposited. When the metal oxide conductor is directly depositedafter the organic layer is formed, the organic layer is largely damaged.Therefore, in the above-mentioned Japanese Unexamined Patent ApplicationPublications, to decrease damage in forming a film, it is considered touse various buffer layers and devise the film forming method. However,the effect thereof is limited, and the reliability and the luminanceefficiency decline. In addition, leakage due to sputtered particles isgenerated. Further, when an additional process is used to decrease thedamage, the cost is increased.

In the case of the device structure having the light resonatorstructure, in general, the optical distance L between the reflectiveface and the semi-transparent face satisfies Mathematical formula 1.L=(m−Φ/2π)λ/2  Mathematical formula 1

In the formula, L represents the optical distance between the reflectiveface and the semi-transparent face, m represents an order (0 or anatural number), Φ represents the sum of the phase shift of thereflected light generated on the reflective face and the phase shift ofthe reflected light generated on the semi-transparent face (rad), and λrepresents the peak wavelength of a spectrum of light desired to beextracted from the semi-transparent face side. In Mathematical formula1, the unit used for L and λ may be common, for example, nm is used.

Between the reflective face and the semi-transparent face, there arepositions (resonant faces) where the extracted luminescence intensitybecomes the maximum. The number of the resonant faces is m+1. When m is1 or more, the half bandwidth of the emission spectrum is largest in thecase that the light emitting face is on the resonant face closest to thereflective face.

In such a light resonator structure, the color purity and theluminescence intensity of the front can be increased. Meanwhile, colorshift and intensity lowering to the view angle are observed. As mbecomes larger, significant view angle dependency is shown. Consideringonly the visual field characteristics, m is ideally 0. However, in thatcase, the organic film thickness becomes thin. Therefore, there is ahigher possibility that the light emitting characteristics are affectedand a defect due to leak is caused.

To solve the foregoing, for example, it is thought that the followingstate is effective. That is, for example, m is 1, and the light emittinglayer is on the resonant face close to the reflective face.

As a method to arrange the light emitting layer on the resonant faceclose to the reflective face, the thickness of electron transport layermay be increased, in the existing device structure including theresonant structure typified by International Publication No. WO01/039554 and Japanese Unexamined Patent Application Publication No.10-177896, that is, in the existing device in which a light-reflectivelower anode, a hole-transport layer, a light emitting layer, an electrontransport layer, and a light-semi-transparent upper cathode are layeredin this order. However, when the thickness of the electron transportlayer made of Alq₃ generally used is increased, the driving voltage isextremely increased, leading to increase of the power consumption of thepanel.

Meanwhile, in the active matrix organic EL drive system panel, it isincreasingly considered to use an amorphous TFT and an organic TFT, inaddition to the low temperature polysilicon TFT used from the past.Depending on the structure of the TFT and the design of the drivecircuit, the reflective electrode on the substrate side is preferably acathode in some cases. However, in the existing organic EL display unithaving the light resonator structure, only the case that the reflectiveelectrode on the substrate side is an anode is known. Thus, in somecases, it is not able to address diversified active drive circuits.

In view of the foregoing, in the invention, it is desirable to providean organic light emitting device capable of improving the lightextraction characteristics while suppressing the driving voltage andimproving the luminescent performance, and a display unit using theorganic light emitting device.

According to an embodiment of the invention, there is provided anorganic light emitting device including a lamination structure thatincludes a cathode, a plurality of layers including a light emittinglayer made of an organic material, and an anode including a metal thinfilm in this order, in which the cathode is reflective and the anode issemi-transparent to light generated in the light emitting layer, and aresonator structure that resonates the light generated in the lightemitting layer between the cathode and the anode. “Transparent” meansthat the transmittance of visible light is 10% to 100%. “Reflective”means that the reflectance of visible light is 10% to 100%.“Semi-transparent” means both transparent characteristics and reflectivecharacteristics are included.

According to an embodiment of the invention, there is provided a displayunit including a plurality of organic light emitting devices. Theplurality of organic light emitting devices are composed of theforegoing organic light emitting devices of the embodiment of theinvention.

The organic light emitting device according to the embodiment of theinvention has the lamination structure in which the reflective cathode,the plurality of layers including the light emitting layer, and thesemi-transparent anode including the metal thin film are layered in thisorder. Therefore, by increasing the thickness of the layer close to theanode in the plurality of layers, the light emitting layer is arrangedon the resonance face close to the cathode where the extractionluminescence intensity is highest in the resonator structure. In theresult, lowering of extracted light intensity and shift to the shortwavelength side depending on the view angle are suppressed withoutincreasing the driving voltage, and high light extraction efficiency canbe obtained.

In the display unit according to the embodiment of the invention, theorganic light emitting device according to the embodiment of theinvention is used. Therefore, the display performance is improved.

The organic light emitting device according to the embodiment of theinvention has the lamination structure in which the reflective cathode,the plurality of layers including the light emitting layer, and thesemi-transparent anode including the metal thin film are layered; andthe resonator structure including the cathode and the anode. Therefore,the light emitting layer in the resonator structure can be optimallypositioned without increasing the driving voltage, the high lightextraction characteristics can be realized while the view angledependency is relaxed, and the luminescent performance can be increased.Further, the display unit according to the embodiment of the inventionincludes the organic light emitting device of the embodiment of theinvention with the high luminescent performance. Therefore, the displayperformance can be improved. In addition, the display unit according tothe embodiment of the invention is extremely suitable for addressing thediversified active drive circuit such as an organic TFT.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing a structure of a display unitaccording to an embodiment of the invention;

FIG. 2 is a cross section showing a structure of an organic lightemitting device shown in FIG. 1;

FIG. 3 is a diagram showing a relation between the absorptance of ametal thin film composing an anode and the emission spectrum intensity;

FIG. 4 is a cross section showing a structure of an organic lightemitting device formed in a comparative example of the invention;

FIG. 5 is a diagram showing results of examples of the invention; and

FIG. 6 is a diagram showing results of the examples of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention will be hereinafter described in detailwith reference to the drawings.

First Embodiment

FIG. 1 shows a cross sectional structure of an organic EL display unitaccording to a first embodiment of the invention. The display unit isused as an ultrathin organic light emitting display in which a drivingpanel 10 and a sealing panel 20 are oppositely arranged, and the wholeareas thereof are bonded together by an adhesive layer 30 made of athermosetting resin or the like. In the driving panel 10, for example,an organic light emitting device 10R for generating red light, anorganic light emitting device 10G for generating green light, and anorganic light emitting device 10B for generating blue light aresequentially provided in a state of matrix on a driving substrate 11made of an insulating material such as glass, with a TFT 12 and aplanarizing film 13 in between.

The TFT 12 is an active device corresponding to the respective organiclight emitting devices 10R, 10G and 10B. The organic light emittingdevices 10R, 10G and 10B are driven by active matrix system. A gateelectrode (not shown) of the TFT 12 is connected to a not-shown scanningcircuit. A source and a drain (either not shown) are connected to awiring 12B provided with an interlayer insulating film 12A made of, forexample, silicon oxide or PSG (Phos-Silicate Glass) in between. Thewiring 12B is connected to the source and the drain of the TFT 12through a not-shown connection hole provided in the interlayerinsulating film 12A, and is used as a signal line. The wiring 12B is,for example, about 1.0 μm thick, and is made of, for example, aluminum(Al) or an aluminum (Al)-copper (Cu) alloy. The structure of the TFT 12is not particularly limited. For example, the structure thereof may bebottom gate type or top gate type.

The planarizing film 13 is a foundation layer for planarizing thesurface of the driving substrate 11 formed with the TFT 12 and foruniformalizing the film thickness of each layer of the organic lightemitting devices 10R, 10G and 10B. The planarizing film 13 is providedwith a connection hole 13A for connecting a cathode 14 of the organiclight emitting devices 10R, 10G and 10B to the wiring 12B.

In the organic light emitting devices 10R, 10G and 10B, for example, acathode 14, an insulating film 15, a display layer 16 having a pluralityof layers including a light emitting layer 16C made of an organicmaterial, and an anode 17 are layered in this order from the drivingsubstrate 11 side with the TFT 12 and the planarizing film 13 inbetween. In the display layer 16, for example, as shown in FIG. 2, anelectron injection layer 16A, an electron transport layer 16B, a lightemitting layer 16C, a hole-transport layer 16D, and a hole-injectionlayer 16E are layered from the cathode 14 side. On the anode 17, aprotective layer 18 is formed if necessary.

Further, in the organic light emitting devices 10R, 10G and 10B, thecathode 14 is reflective for light generated in the light emitting layer16C, while the anode 17 is semi-transparent. The cathode 14 and theanode 17 compose a resonator structure for resonating the lightgenerated in the light emitting layer 16C.

That is, the organic light emitting devices 10R, 10G and 10B have aresonator structure to resonate the light generated in the lightemitting layer 16C and extract the light from a second end P2 side,where the end face of the cathode 14 on the light emitting layer 16Cside is a first end P1, the end face of the anode 17 on the lightemitting layer 16C side is the second end P2, and the display layer 16is a resonant section. When the organic light emitting devices 10R, 10Gand 10B have the resonator structure as above, the light generated inthe light emitting layer 16C produces multiple interference and works asa kind of narrow band-pass filter. Thereby, the half bandwidth of thespectrum of the extracted light is reduced, and the color purity can beimproved. Outside light entering from the sealing substrate 21 side canbe also attenuated by the multiple interference. The reflectance of theoutside light in the organic light emitting devices 10R, 10G and 10B canbe extremely decreased by combining with a color filter 22 describedlater, a wave plate, or a polarizing plate (not shown).

To that end, it is preferable that the optical distance L between thefirst end (reflective face) P1 and the second end (semi-transparentface) P2 of the resonator satisfy Mathematical formula 2, and a resonantwavelength of the resonator (peak wavelength of the spectrum of theextracted light) corresponds with the peak wavelength of the spectrum ofthe light desired to be extracted.L=(m−Φ/(2π)λ/2  Mathematical formula 2

In the formula, L represents the optical distance between the first endP1 and the second end P2, m represents an order (0 or a natural number),Φ represents the sum of the phase shift Φ₁ of the reflected lightgenerated at the first end P1 and the phase shift Φ₂ of the reflectedlight generated at the second end P2 (Φ=Φ₁+Φ₂) (rad), and λ representsthe peak wavelength of the spectrum of the light desired to be extractedfrom the second end P2 side. In Mathematical formula 2, the unit usedfor L and λ may be common, for example, nm is used.

Between the first end P1 and the second end P2, there are positions(resonant faces) where the extracted luminescence intensity becomes themaximum. The number of such positions is m+1. When m is 1 or more, thehalf bandwidth of the emission spectrum is largest in the case that thelight emitting layer 16C is on the resonant face closest to the firstend P1, the lowering of the intensity of the extracted light dependingon the view angle is suppressed, and the short wavelength shift of theextracted light is decreased.

Though the order m is not particularly limited, m is preferably 1, thatis, two resonant faces exist, and the light emitting layer 16C isarranged on the resonant face close to the first end P1. As describedabove, as m becomes larger, the view angle dependency is increased.Meanwhile, when m is 0, the thickness of the display layer 16 becomessmall, and thus shortcomings of light emitting characteristics such ascurrent leakage easily occur.

As described above, the display unit has the lamination structure inwhich the cathode 14, the display layer 16 including the light emittinglayer 16C, and the anode 17 are layered in this order from the drivingsubstrate 11 side. Thereby, in this display unit, by increasing thethickness of the hole-transport layer 16D, the light emitting layer 16Ccan be arranged on the resonant face close to the first end P1. Thereby,the light extraction characteristics can be improved without increasingthe driving voltage, and the luminescent performance can be improved.

The cathode 14 becoming the first end P1 of the resonator structuredesirably has the high reflectance as much as possible, in order toincrease the luminance efficiency. Further, since the cathode 14 is anelectron injection electrode, an electron injection barrier to thedisplay layer 16 is preferably small, and is desirably made of a metalwith the small work function. The thickness of the cathode 14 in thelamination direction (hereinafter simply referred to as thickness) isfrom 30 nm to 2000 nm, and is made of an alloy of an alkali metal or analkali earth metal such as lithium (Li), magnesium (Mg), and calcium(Ca); and a metal such as silver (Ag), aluminum (Al), and indium (In).Further, the cathode 14 may have a lamination structure including alayer of the foregoing alkali metal or the foregoing alkali earth metaland a layer of the foregoing metal.

The cathode 14 can be also made of a metal, a metal oxide or the likewith the relatively large work function, by using various surfacetreatments or the after-mentioned electron injection layer 16A. Thecathode 14 may have a lamination structure including, for example, athin film made of a metal with the small work function or a dope layerincluding a metal with the small work function; and a transparentelectrode made of a metal oxide such as tin oxide (SnO₂), ITO (Indiumtin Oxide), zinc oxide, and titanium oxide.

Meanwhile, the anode 17 as the second end P2 is desirably designed as asemi-transparent reflective layer so that the total of the reflectanceand the transmittance is close to 100% as much as possible and theabsorptance is small as much as possible in order to decrease loss dueto absorption. Further, the anode 17 should function as an electrode,and should have the conductivity sufficient for supplying electron holesto the organic EL device in the thin film as well.

As a material of the anode 17, for example, a metal thin film made of analloy of an alkali metal or an alkali earth metal such as magnesium(Mg), calcium (Ca) and sodium (Na) and silver (Ag) is preferable. Inparticular, a metal thin film made of an alloy containing magnesium (Mg)and silver (Ag) is more preferable. The metal thin film made of an alloycontaining magnesium (Mg) and silver (Ag) is able to be stablyvacuum-deposited, even the thickness of thereof is about 5 nm to 10 nm,the organic EL device can be driven. Therefore, such a metal thin filmis suitable as an electrode on the light extraction side in the lightresonator structure. The anode 17 made of the alloy of magnesium (Mg)and silver (Ag) is able to be simply formed by a film-forming methodthat does not damage an organic film much such as resistance heatingdeposition. In the result, in this case, the defect is decreased andlight emission with the high reliability can be obtained, compared tothe organic EL device of the related art described in JapaneseUnexamined Patent Application Publication Nos. 2003-203781, 2003-203783,2003-323987, 2004-146198, 2004-152542, 2005-032618, 2005-276542, and2005-530320. Further, the thickness of the metal thin film of the anode17 is from 5 nm to about 10 nm or to about 20 nm. Therefore, even when adefect is generated in the display layer 16, there is less possibilitythat the metal material of the anode 17 intrudes in the defect, and thusa non-light emitting defect due to short circuit can be prevented.

A single metal thin film made of, for example, aluminum (Al), silver(Ag), gold (Au), or copper (Cu) can be used as the anode 17. However, itis difficult to form an ultrathin film with the conductivity capable ofdriving the organic light emitting devices 10R, 10G and 10B with such afilm being about 10 nm thick.

The absorptance a of the metal thin film composing such an anode 17preferably satisfies Mathematical formula 3, and is more preferablyunder 40%. Thereby, the resonator structure can be effectivelyfunctioned, and the light extraction efficiency can be increased.α(%)=100−(R+T)  Mathematical formula 3

In the formula, α represents the light absorptance (%) in the wavelengthregion from 400 nm to 800 nm of the metal thin film, R represents thereflectance (%) of the metal thin film to the display layer 16 side, andT represents the transmittance (%) of the metal thin film.

FIG. 3 is a result of calculating the emission spectrums in the casethat the absorptance of the metal thin film composing the anode 17 in550 nm is 20% and 40%. In the case that the absorptance is 20%, theanode 17 is 10 nm thick, and is made of a metal thin film made of anMg—Ag alloy. As evidenced by FIG. 3, the luminescence intensity in thecase that the absorptance is 40% is decreased down to the degree aboutone half (½) of the case that the absorptance is 20%. That is, when theabsorptance of the metal thin film composing the anode 17 is under 40%,the efficiency can be increased, and it is extremely advantageous inorder to maintain the display quality.

The insulating film 15 shown in FIG. 1 is intended to secure insulationproperties between the cathode 14 and the anode 17, and to accuratelyobtain a desired form of light emitting regions in the organic lightemitting devices 10R, 10G and 10B. The insulating film 15 is made of,for example, a photosensitive resin such as polyimide. The insulatingfilm 15 is provided with an aperture 15A corresponding to the lightemitting regions.

The electron injection layer 16A shown in FIG. 2 is intended to increasethe electron injection efficiency. The electron transport layer 16B isintended to increase the electron transport efficiency to the lightemitting layer 16C. The light emitting layer 16C generates light byelectron-hole recombination by applying an electric field. Thehole-transport layer 16D is intended to increase the electron holetransport efficiency to the light emitting layer 16C. The hole-injectionlayer 16E is intended to increase the electron hole injectionefficiency. Of the foregoing, layers other than the light emitting layer16C may be provided if necessary. Further, the display layer 16 may havea different structure according to the light emitting color of theorganic light emitting devices 10R, 10G and 10B.

The electron injection layer 16A is preferably made of an alloy of analkali metal or an alkali earth metal such as lithium (Li), magnesium(Mg), and calcium (Ca) and a metal such as silver (Ag), aluminum (Al),and indium (In), specifically made of an Mg—Ag alloy. Further, theelectron injection layer 16A is preferably made of a compound of analkali metal or an alkali earth metal such as lithium (Li), magnesium(Mg), and calcium (Ca) and halogen such as fluorine and bromine oroxygen, specifically LiF. Further, the electron injection layer 16A maybe made of a material in which an alkali metal such as magnesium (Mg) isadded to an electron transport organic material such as 8-quinolinolealuminum complex (Alq₃). The electron injection layer 16A may have astructure in which two or more of the foregoing films are layered.

When the electron injection layer 16A is made of, for example, ahalogenide of an alkali metal such as LiF, a halogenide of an alkaliearth metal, an oxide of an alkali metal, or an oxide of an alkali earthmetal, the thickness of the electron injection layer 16A is preferablyfrom 0.3 nm to 1.3 nm. Thereby, the driving voltage can be decreased,and the luminance efficiency can be increased.

The electron transport layer 16B is, for example, from 5 nm to 50 nm,and is made of Alq₃.

The material of the light emitting layer 16C is different according tothe light emitting color of the organic light emitting devices 10R, 10Gand 10B. The light emitting layer 16C of the organic light emittingdevice 10R is, for example, 10 nm to 100 nm thick, and is made of acompound in which 40 volume % of2,6-bis[4-[N-(4-methoxyphenyl)-N-phenyl]aminostyryl]naphthalene-1,5-dicarbonitrile(BSN—BCN) is mixed with Alq₃. The light emitting layer 16C of theorganic light emitting device 10G is, for example, 10 nm to 100 nmthick, and is made of a compound in which 3 volume % of coumarine 6 ismixed with Alq₃. The light emitting layer 16C of the organic lightemitting device 10B is, for example, 10 nm to 100 nm thick, and is madeof a compound in which 1 volume % of perylene is mixed with ADN(9,10-di(2-naphthyl)anthracene.

The hole-transport layer 16D is, for example, 5 nm to 300 nm thick, andis made of bis[(N-naphthyl)-N-phenyl]benzidine (α-NPD).

The hole injection layer 16E is preferably, for example, 4 nm thick ormore, and is preferably made of the pyrazine derivative shown inChemical formula 1. In addition, an oxide such as titanium oxide,niobium oxide, molybdenum oxide metal is also preferable. The Mg—Agalloy composing the anode 17 is generally a material used as an electroninjection electrode, and the work function thereof is about 3.7 eV,which is small. The foregoing material is preferably used, since therebythe anode 17 made of the Mg—Ag alloy can function as a hole-injectionelectrode. Further, the anode 17 made of the Mg—Ag alloy can beprevented from contacting with an organic material composing the displaylayer 16 to generate chemical change, increasing light absorption, andlosing the function as the electrode.

Specially, a hexaazatriphenylene derivative shown in Chemical formula 2or molybdenum oxide is more preferable. Such materials can be easilyformed by resistance heating type vacuum deposition method. In addition,there is no possibility that the conductivity of the anode 17 made ofthe Mg—Ag alloy is lost due to such materials.

The protective layer 18 is, for example, 500 nm to 10000 nm thick, andis a passivation film made of a transparent derivative. The protectivelayer 18 is made of, for example, silicon oxide (SiO₂), silicon nitride(SiN) or the like.

The sealing panel 20 is located on the anode 17 side of the drivingpanel 10, and has a sealing substrate 21 that seals the organic lightemitting devices 10R, 10G and 10B together with an adhesive layer 30.The sealing substrate 21 is made of a material such as glass transparentto light generated in the organic light emitting devices 10R, 10G and10B. The sealing substrate 21 is, for example, provided with a colorfilter 22 and a reflected light absorption film 23 as black matrix. Thecolor filter 22 and the reflected light absorption film 23 extract thelight generated in the organic light emitting devices 10R, 10G and 10B,absorb outside light reflected by the organic light emitting devices10R, 10G and 10B and the wiring therebetween, and improves the contrast.

Though the color filter 22 and the reflected light absorption film 23may be provided on either side of the sealing substrate 21, the colorfilter 22 and the reflected light absorption film 23 are preferablyprovided on the driving panel 10 side. Thereby, the color filter 22 andthe reflected light absorption film 23 are not exposed on the surfaceand can be protected by the adhesive layer 30. The color filter 22 has ared filter 22R, a green filter 22G, and a blue filter 22B. The redfilter 22R, the green filter 22G, and the blue filter 22B aresequentially arranged according to the organic light emitting devices10R, 10G and 10B.

The red filter 22R, the green filter 22G, and the blue filter 22B are,for example, respectively rectangle, and formed with no spacetherebetween. The red filter 22R, the green filter 22G, and the bluefilter 22B are respectively made of a resin mixed with a pigment. Thered filter 22R, the green filter 22G, and the blue filter 22B areadjusted so that the light transmittance in the targeted red, green, orblue wavelength band becomes high and the light transmittance in theother wavelength bands becomes low by selecting the pigment.

The reflected light absorption film 23 is provided along the borderbetween the red filter 22R/the green filter 22G/the blue filter 22B. Thereflected light absorption film 23 is made of, for example, a blackresin film in which a black pigment is mixed therein and the opticaldensity is 1 or more, or a thin film filter using interference of a thinfilm. Of the foregoing, the black resin film is preferably used, sincesuch a film can be formed inexpensively and easily. In the thin filmfilter, for example, one or more thin films made of a metal, a metalnitride, or a metal oxide are layered, and light is attenuated by usingthe interference of the thin films. As the thin film filter,specifically, a lamination in which chromium and chromium oxide(III)(Cr₂O₃) are alternately layered can be cited.

The display unit can be manufactured, for example, as follows.

First, the reflected light absorption film 23 made of the foregoingmaterial is formed on the sealing substrate 21 made of the foregoingmaterial, and patterned into a given shape. Next, the sealing substrate21 is coated with a material of the red filter 22R by spin coating orthe like, the resultant is patterned by photolithography technique andfired, and thereby the red filter 22R is formed. In patterning, theperipheral edge portion of the red filter 22R preferably covers part ofthe reflected light absorption film 23. It is difficult to pattern withhigh precision without covering the reflected light absorption film 23.In addition, the portion of the red filter 22R covering the reflectedlight absorption film 23 does not affect the image display.Subsequently, in the same manner as in the red filter 22R, the bluefilter 22B and the green filter 22G are sequentially formed. Thereby,the sealing panel 20 is formed.

Then, for example, the TFT 12, the interlayer insulating film 12A, andthe wiring 12B are formed over the driving substrate 11 made of theforegoing material. The planarizing film 13 made of the foregoingmaterial is formed over the whole area by, for example, spin coatmethod. Then, the planarizing film 13 is formed into a given shape byproviding exposure and development and the connection hole 13A isformed, and fired.

Next, the cathode 14 made of the foregoing material is formed by, forexample, sputtering or deposition. Then, etching is made to form thecathode 14 into a given shape.

Subsequently, the whole area of the driving substrate 11 is coated witha photosensitive resin, which is formed by, for example,photolithography method to provide the aperture 15A in the portioncorresponding to the cathode 14. The resultant is fired to form theinsulating film 15.

After that, corresponding to the aperture 15A of the insulating film 15,the electron injection layer 16A, the electron transport layer 16B, thelight emitting layer 16C, the hole-transport layer 16D, thehole-injection layer 16E, and the anode 17 that have the foregoingthickness and are made of the foregoing material are sequentially formedby, for example, deposition to form the organic light emitting devices10R, 10G and 10B as shown in FIG. 2. Subsequently, the protective layer18 is formed on the organic light emitting devices 10R, 10G and 10B ifnecessary. Thereby, the driving panel 10 is formed.

After the sealing panel 20 and the driving panel 10 are formed, theadhesive layer 30 made of the foregoing material is formed by coatingover the driving substrate 11 on the side where the organic lightemitting devices 10R, 10G and 10B are formed. The driving panel 10 andthe sealing substrate 20 are bonded to each other with the adhesivelayer 30 in between. Consequently, the display unit shown in FIG. 1 iscompleted.

In the display unit, when a given voltage is applied between the anode17 and the cathode 14 in the respective organic light emitting devices10R, 10G and 10B, a current is injected in the light emitting layer 16C,electron-hole recombination occurs, and thereby light is generated. Thelight is multiply reflected between the anode 17 and the cathode 14, andextracted through the semi-transparent anode 17, the color filter 22,and the sealing substrate 21. In this embodiment, the reflective cathode14, the display layer 16 including the light emitting layer 16C, and thesemi-transparent anode 17 including a metal thin film are sequentiallylayered in this order. Thereby, by increasing the thickness of thehole-transport layer 16D, the light emitting layer 16C can be arrangedon the resonant face close to the cathode 14 in the resonator structure.Therefore, lowering of the intensity of the extracted light and theshort wavelength shift depending on the view angle are suppressed. Thus,the light generated in the light emitting layer 16C can be extractedwith the high extraction efficiency. Further, selection of the materialof the hole-transport layer 16D is more extensive than that of theelectron transport material. In addition, the electron hole mobility ofthe material of the hole-transport layer is relatively higher than theelectron mobility of the electron transport material. Therefore, evenwhen the thickness of the hole-transport layer 16D is increased and thelight emitting layer 16D is arranged on the resonant face close to thefirst end P1, the driving voltage hardly rises.

Further, the TFT 12, the wiring 12B and the like that affect theaperture ratio are provided on the reflective cathode 14 side, andthereby the high aperture ratio can be maintained. In addition, byincreasing the thickness of the hole-transport layer 16D, coating effecton the substrate by the organic film of the display layer 16 isincreased, and thus a defect resulting from defective film-forming onthe cathode 14, attachment of foreign matters thereon and the like, andshort circuit resulting from loss of the organic film are prevented.

Meanwhile, in the past, the light-reflective anode, the hole-transportlayer, the light emitting layer, the electron transport layer, and thelight-semi-transparent cathode are layered in this order over thesubstrate. Therefore, to arrange the light emitting layer on theresonant face close to the anode, the electron transport layer isthickened. In the result, the driving voltage is significantlyincreased, leading to increase of the power consumption of the panel.

As above, in this embodiment, in the organic light emitting devices 10R,10G and 10B having a resonator structure, the reflective cathode 14, thedisplay layer 16 including the light emitting layer 16C, and thesemi-transparent anode 17 are layered in this order. Therefore, it ispossible to suppress the view angle dependency without increasing thedriving voltage, improve the light extraction characteristics, andimprove the luminescent performance. In the result, the display unitincluding the organic light emitting devices 10R, 10G and 10B with thehigh luminescent performance can improve the display performance. Inparticular, the display unit in this embodiment is extremely suitablefor a case using an organic TFT or the like as the TFT 12.

Further, the thickness of the hole-transport layer 16D can be increased.Therefore, defects due to short circuit can be decreased, and thereliability can be improved.

Further, the TFT 12, the wiring 12B and the like that affect theaperture ratio are provided on the reflective cathode 14 side, andthereby the high aperture ratio can be maintained.

EXAMPLES

Further, specific examples of the invention will be described in detail.

Examples 1-1 and 1-2

The organic light emitting devices 10B were formed in the same manner asin the foregoing embodiment.

First, the cathode 14 made of an aluminum-neodymium alloy being 100 nmthick was formed over the driving substrate 11 made of glass. Next, theinsulating film 15 made of the foregoing organic insulating material wasformed. The insulating film 15 was patterned and thereby the aperture15A of 2 mm×2 mm was provided corresponding to the light emitting regionto expose the cathode 14.

Subsequently, the metal mask having the aperture corresponding to theexposed portion of the cathode 14 was arranged in the vicinity of thedriving substrate 11. With the use of vacuum vapor deposition methodunder the vacuum of 10⁻⁴ Pa or less, a co-vapor deposition film ofmagnesium (Mg) and silver (Ag) (Mg:Ag=10:1) being 2 nm thick and a LiFfilm being 0.3 nm thick were layered to form the electron injectionlayer 16A.

After that, with the use of vacuum vapor deposition method again, theelectron transport layer 16B, the light emitting layer 16C, thehole-transport layer 16D, and the electron injection layer 16E that weremade of the foregoing material were sequentially formed, and thereby thedisplay layer 16 was formed. At that time, as a material of thehole-injection layer 16E, the hexaazatriphenylene derivative shown inChemical formula 2 was used in Example 1-1, and molybdenum oxide wasused in Example 1-2. The thickness of each layer was set so that theoptical distance L between the cathode 14 and the anode 17 satisfiedMathematical formula 2, and the blue light emission was amplified by theresonator structure. That is, the electron transport layer 16B was 20 nmthick, the light emitting layer 16C was 25 nm thick, the hole-transportlayer 16D was 130 nm thick, and the hole-injection layer 16E was 8 nmthick.

After the display layer 16 was formed, with the use of vacuum vapordeposition method again, as the anode 17, a co-vapor deposition film ofmagnesium (Mg) and silver (Ag) (Mg:Ag=10:1) being 10 nm thick wasformed. Consequently, the organic light emitting device 10B shown inFIG. 2 was obtained.

Further, a film made of the hexaazatriphenylene derivative shown inChemical formula 2 being 8 nm thick and an Mg—Ag alloy film (Mg:Ag=10:1)being 10 nm thick were sequentially layered over a quartz glass plate,and the transmittance and the reflectance in the wavelength of 550 nmwere examined. In the result, semi-transparent characteristics with thetransmittance of 41% and the reflectance of 39% were observed. Formolybdenum oxide, examination was made similarly. That is, a film madeof molybdenum oxide being 8 nm thick and an Mg—Ag alloy film(Mg:Ag=10:1) being 10 nm thick were sequentially layered over a quartzglass plate, and the transmittance and the reflectance in the wavelengthof 550 nm were examined. In the result, semi-transparent characteristicswith the transmittance of 46% and the reflectance of 23% were observed.

As Comparative example 1, an organic light emitting device that has theexisting top emission structure in which a reflective anode 117, anelectron injection layer 116E, a hole-transport layer 116D, a lightemitting layer 116C, an electron transport layer 116B, an electroninjection layer 116A, and a semi-transparent cathode 114 are layered inthis order from a driving substrate 111 side as shown in FIG. 4, andthat generates blue light was formed.

That is, the anode 117 made of an aluminum-neodymium alloy being 100 nmthick was formed over the driving substrate 111 made of glass. Next, aninsulating film (not shown) was formed in the same manner as in Examples1-1 and 1-2. Subsequently, the hole-injection layer 116E made of thehexaazatriphenylene derivative shown in Chemical formula 2, thehole-transport layer 116D made of α-NPD, the light emitting layer 116Cmade of a material similar to that of Example 1-1, the electrontransport layer 116B made of Alq₃, and the electron injection layer 116Amade of LiF were sequentially formed. The thickness of each layer wasset so that the optical distance L between the anode 117 and the cathode114 satisfied Mathematical formula 2, and the blue light emission wasamplified by the resonator structure. That is, the hole-injection layer116E was 8 nm thick, the hole-transport layer 116D was 140 nm thick, thelight emitting layer 116C was 25 nm thick, the electron transport layer116B was 20 nm thick, and the electron injection layer 116A was 0.3 nmthick. After that, the cathode 114 made of a co-vapor deposition film ofmagnesium (Mg) and silver (Ag) (Mg:Ag=10:1) being 10 nm thick wasformed.

For the obtained organic light emitting devices of Examples 1-1, 1-2 andComparative example 1, the current density-voltage characteristics andthe emission spectrums where the current density was 10 mA/cm² wereexamined. The results are shown in FIG. 5 and FIG. 6.

As evidenced by FIG. 5 and FIG. 6, in Examples 1-1 and 1-2, the electronhole injection characteristics and the luminescence intensity werepreferable almost equally to those of Comparative example 1, and thedriving voltage was not increased. That is, it was found that in theorganic light emitting device 10B having the resonator structure, whenthe reflective cathode 14, the display layer 16 including the lightemitting layer 16C, and the semi-transparent anode 17 were layered inthis order, the organic light emitting device 10B with the superiorlight extraction characteristics and the high luminescent performancecan be realized without increasing the driving voltage.

Further, in Example 1-1, both the electron hole injectioncharacteristics and the luminescence intensity were more preferable thanin Example 1-2. That is, it was found that when the hole-injection layer16E was made of the hexaazatriphenylene derivative shown in Chemicalformula 2, the electron hole injection characteristics and theluminescence intensity could be more improved.

Examples 2-1 to 2-4

The organic light emitting devices 10B were formed in the same manner asin Example 1-1, except that the thickness of the hole-injection layer16E was changed as shown in Table 1. For the obtained organic lightemitting devices 10B of Examples 2-1 to 2-4, the driving voltage and theluminance efficiency at the current density of 10 mA/cm² were examined.The results are shown in Table 1 together.

TABLE 1 Thickness of Driving voltage Luminance efficiency hole-injectionat 10 mA/cm² at 10 mA/cm² layer (nm) (V) (cd/A) Example 2-1 2 19.9 0.14Example 2-2 3 20.0 1.06 Example 2-3 4 6.3 5.77 Example 2-4 8 5.2 5.16

As evidenced by Table 1, in Examples 2-3 and 2-4 in which the thicknessof the hole-injection layer 16E was 4 nm and 8 nm, the driving voltagewas lower and the luminance efficiency was higher than in Examples 2-1and 2-2 in which the thickness of the hole-injection layer 16E was 2 nmand 3 nm. That is, it was found that when the thickness of thehole-injection layer 16E was 4 nm or more, high luminance efficiencycould be obtained with the lower driving voltage.

Examples 3-1 to 3-8

The organic light emitting devices 10B were formed in the same manner asin Example 1-1, except that the thickness of the LiF film of theelectron injection layer 16A was changed as shown in Table 2. For theobtained organic light emitting devices 10B of Examples 3-1 to 3-8, thedriving voltage and the luminance efficiency at the current density of10 mA/cm² were examined. The results are shown in Table 2 together.

TABLE 2 Thickness of LiF Driving voltage Luminance efficiency film at 10mA/cm² at 10 mA/cm² (nm) (V) (cd/A) Example 3-1 0 7.6 4.35 Example 3-20.3 6.1 5.19 Example 3-3 0.6 5.3 5.12 Example 3-4 1.0 6.2 5.15 Example3-5 1.3 6.2 5.24 Example 3-6 1.6 6.7 5.06 Example 3-7 2.0 6.7 4.71Example 3-8 2.5 7.1 4.62

As evidenced by Table 2, in Examples 3-2, 3-3, 3-4, and 3-5 in which thethickness of the LiF film of the electron injection layer 16A was 0.3nm, 0.6 nm, 1.0 nm, and 1.3 nm, respectively, the driving voltage waslower and the luminance efficiency was higher than in Example 3-1 inwhich the thickness of the LiF film of the electron injection layer 16Awas 0 nm and in Examples 3-6, 3-7, and 3-8 in which the thickness of theLiF film of the electron injection layer 16A was 1.6 nm, 2.0 nm, and 2.5nm, respectively. In particular, in Example 3-3 in which the thicknessof the LiF film of the electron injection layer 16A was 0.6 nm, thedriving voltage was the minimum, which was preferable in terms ofreduction in the power consumption as well. In a general devicestructure in which the anode, the display layer including a lightemitting layer, and the cathode are layered in this order from thedriving substrate side (refer to Comparative example 1), the thicknessof the electron injection layer made of LiF is most preferably about 0.3nm. Meanwhile, in these examples, since the cathode 14, the displaylayer 16, and the anode 17 are layered in this order from the drivingsubstrate 11 side, diffusion of LiF into the electron transport layer16B made of Alq₃ was small. Therefore, it is thought that increasing thethickness of the LiF film in the electron injection layer 16A more thanin the general structure was appropriate in order to improve theelectron injection characteristics.

That is, it was found that when the thickness of the LiF film of theelectron injection layer 16A was 0.3 nm to 1.3 nm, high luminanceefficiency could be obtained with the lower driving voltage. It isexpected that not only in the case of using LiF, but also in the case ofusing a halogenide of other alkali metal, a halogenide of an alkaliearth metal, an oxide of an alkali metal, or an oxide of an alkali earthmetal, effects similar to those of these examples may be obtained.

Examples 4-1 to 4-5

The organic light emitting devices 10B were formed in the same manner asin Example 1-1, except that the structure of the electron injectionlayer 16A was different from that of Example 1-1. That is, in Example4-1, the electron injection layer 16A was made of a LiF film being 0.6nm thick. In Example 4-2, the electron injection layer 16A had astructure in which an Mg—Ag alloy film being 2 nm thick and a LiF filmbeing 0.6 nm thick were layered in this order from the cathode 14 side.In Example 4-3, the electron injection layer 16A had a structure inwhich an Mg—Ag alloy film being 2 nm thick, a LiF film being 0.6 nmthick, and a mixed film in which 5 volume % of magnesium (Mg) was addedto Alq₃ being 5 nm thick were layered in this order from the cathode 14side. In Example 4-4, the electron injection layer 16A had a structurein which an Mg—Ag alloy film being 2 nm thick, a mixed film in which 5volume % of magnesium (Mg) was added to Alq₃ being 5 nm thick, and a LiFfilm being 0.6 nm thick were layered in this order from the cathode 14side. In Example 4-5, the electron injection layer 16A had a structurein which an Mg—Ag alloy film being 2 nm thick and a mixed film in which5 volume % of magnesium (Mg) was added to Alq₃ being 5 nm thick werelayered in this order from the cathode 14 side. The thickness of theelectron transport layer 16B was 20 nm in Examples 4-1 and 4-2, and 15nm in Examples 4-3 to 4-5.

For the obtained organic light emitting devices 10B of Examples 4-1 to4-5, the driving voltage and the luminance efficiency at the currentdensity of 10 mA/cm² were examined. The results are shown in Table 3together.

TABLE 3 Driving Luminance voltage at efficiency Structure of electron 10mA/cm² at 10 mA/cm² injection layer (V) (cd/A) Example 4-1 LiF 0.6 nm13.1 2.44 Example 4-2 Mg—Ag 2 nm/LiF 0.6 nm 6.5 4.70 Example 4-3 Mg—Ag 2nm/LiF 0.6 nm/ 5.2 4.53 Alq₃ + Mg (5%) 5 nm Example 4-4 Mg—Ag 2nm/Alq₃ + Mg 5.1 4.22 (5%) 5 nm/LiF 0.6 nm Example 4-5 Mg—Ag 2 nm/Alq₃ +Mg 6.8 3.53 (5%) 5 nm

As evidenced by Table 3, in Examples 4-2 to 4-5 in which the electroninjection layer 16A had a lamination structure including the Mg—Ag alloyfilm, the driving voltage was lower and the luminance efficiency washigher than in Example 4-1 in which the electron injection layer 16A wasmade of only the LiF film and did not include the Mg—Ag alloy film. Inparticular, in Examples 4-3 and 4-4 in which the electron injectionlayer 16A had the lamination structure including the Mg—Ag alloy film,the mixed film in which 5 volume % of magnesium (Mg) was added to Alq₃,and the LiF film, both the driving voltage and the luminance efficiencywere favorable. That is, it was found that when the electron injectionlayer 16A was made of the Mg—Ag alloy, high luminance efficiency couldbe obtained with the lower driving voltage. In addition, it was foundthat when the electron injection layer 16A was made of a material inwhich 5 volume % of magnesium (Mg) was added to Alq₃, high luminanceefficiency could be obtained with the further lower driving voltage.

While the invention has been described with reference to the embodimentand the examples, the invention is not limited to the foregoingembodiment and the foregoing examples, and various modifications may bemade. For example, the material, the thickness, the film-forming method,the film-forming conditions and the like of each layer are not limitedto those described in the foregoing embodiment, but other material,other thickness, other film-forming method, and other film-formingconditions may be adopted. For example, the driving substrate 11 may bemade of silicon (Si) or a plastic instead of glass. Further, the drivingsubstrate 11 is not necessarily the TFT substrate.

Further, the invention is not limited to the active matrix drive systemdisplay unit, but can be also applied to the simple matrix drive systemdisplay unit.

In addition, in the foregoing embodiment and the foregoing examples, thestructure of the organic light emitting devices 10R, 10G and 10B hasbeen specifically described. However it is not necessary to provide alllayers such as the protective layer 18, and other layer may be furtherprovided. For example, the cathode 14 can have two-layer structure inwhich an transparent conductive film is layered on a dielectricmultilayer film or a reflective film such as Al. In this case, the endface of the reflective film on the light emitting layer side forms theend of a resonant section, and the transparent conductive film formspart of the resonant section.

Further, in the foregoing embodiment and the foregoing examples, thedescription has been given of the case that the organic light emittingdevices 10R, 10G and 10B have the resonator structure to resonate thelight generated in the light emitting layer 16C and extract the lightfrom the second end P2 side, where the end face of the cathode 14 on thelight emitting layer 16C side is the first end P1, the end face of theanode 17 on the light emitting layer 16C side is the second end P2, andthe display layer 16 is the resonant section. However, the first end P1and the second end P2 may be formed on the interface between layers madeof two types of materials with the refractive index different from eachother. For example, in the foregoing embodiment and the foregoingexamples, the description has been given of the case that the anode 17is made of the semi-transparent metal thin film. However, the anode 17may have a structure in which a semi-transparent metal thin film and atransparent electrode are sequentially layered from the anode 14 side.The transparent electrode is intended to decrease the electricresistance of the semi-transparent metal thin film, and is made of aconductive material having translucency sufficient for the lightgenerated in the light emitting layer. As a material of the transparentelectrode, for example, ITO, or a compound containing indium, zinc (Zn),and oxygen is preferable. Thereby, even when film forming is made at theroom temperatures, favorable conductivity can be obtained. The thicknessof the transparent electrode can be, for example, from 30 nm to 1000 nm.In this case, a resonator structure in which the semi-transparent metalthin film is used as one end, the other end is provided in the positionfacing the semi-transparent metal thin film with the transparentelectrode in between, and the transparent electrode is used as aresonant section. Further, it is preferable that such a resonatorstructure is provided, the organic light emitting devices 10R, 10G and10B are covered with a protective film, and the protective film is madeof a material having the refractive index almost the same as that of thematerial of the transparent electrode. Thus, the protective film canbecome part of the resonant section.

In addition, the invention can be also applied to a case in which theanode 17 is composed of a transparent electrode, the reflectance of theend face of the transparent electrode on the opposite side of thedisplay layer 16 is large, and a resonator structure in which the endface of the cathode 14 on the light emitting layer 16C side is the firstend, and the end face of the transparent electrode on the opposite sideof the display layer 16 is the second end. For example, it is possiblethat the transparent electrode is contacted with the air layer, thereflectance of the interface between the transparent electrode and theair layer is large, and the interface is used as the second end.Otherwise, it is possible that the reflectance of the interface with theadhesive layer is large, and the interface is used as the second end.Otherwise, it is possible that the organic light emitting devices 10R,10G and 10B are covered with a protective film, the reflectance of theinterface with the protective layer is large, and the interface is usedas the second end.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alternations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An organic light emitting device on a substratecomprising: a lamination structure that includes, in this order, (a) acathode, (b) a plurality of layers including an ordered arrangement of(i) an electron injection layer, (ii) an electron transport layer, (iii)a light emitting layer made of an organic material, (iv) a holetransport layer, and (v) a hole injection layer, and (c) an anodeincluding a metal thin film with a top surface and a bottom surface,wherein, a resonator structure between the cathode and the anode isconfigured to resonate light generated in the light emitting layer suchthat the light is emitted through the top surface of the anode and in adirection opposite to that of the cathode and the substrate, the cathodeis reflective, the anode is semi-transparent to the light generated inthe light emitting layer, the anode comprises a magnesium-silver alloyin which a ratio of Mg:Ag is 10:1, the anode having a thickness that isless than a thickness of the cathode, the thickness of the anode being10 nm, the anode is disposed above the hole injection layer such thatthe bottom surface of the anode is in contact with the hole injectionlayer and faces the substrate, the electron injection layer is betweenthe electron transport layer and the cathode such that the electroninjection layer has one surface in contact with the electron transportlayer and another surface in contact with the cathode, the electroninjection layer is a laminate structure that includes a first filmcomprising a magnesium-silver alloy and a second film comprising analkali metal or an alkali earth metal, the cathode is between theelectron injection layer and the substrate, a thickness of the electrontransport layer is greater than a thickness of the electron injectionlayer, the plurality of layers are formed such that the light emittinglayer is closer in distance to the cathode than the anode in a thicknessdirection, and a light absorptance a of the metal thin film satisfiesα=100−(R+T), where a is a light absorptance percentage in a wavelengthband from 400 nm to 800 nm of the metal thin film, R represents areflectance percentage of the metal thin film to a side of the pluralityof layers, and T represents a transmittance percentage of the metal thinfilm.
 2. The organic light emitting device according to claim 1, whereinthe hole injection layer contains a hexaazatriphenylene derivativerepresented by

where R represents (a) an alkyl group, (b) an alkyloxy group, (c) adialkyl amine group with a hydrogen and carbon number of 1 to 10, (d) F,(e) Cl, (f) Br, (g) I, or (h) CN.
 3. The organic light emitting deviceaccording to claim 1, wherein the hole injection layer is made of ametal oxide.
 4. The organic light emitting device according to claim 1,wherein the light absorptance a of the metal thin film is under 40% in awavelength region from 400 nm to 800 nm.
 5. The organic light emittingdevice according to claim 1, wherein an electron mobility of the holetransport layer is relatively higher than an electron mobility of theelectron transport layer.
 6. The organic light emitting device accordingto claim 1, wherein the first film and the second film are layered inthis order from the cathode.
 7. The organic light emitting deviceaccording to claim 1, wherein the first film is thicker than the secondfilm.
 8. The organic light emitting device of claim 1, wherein the holeinjection layer contains a pyrazine derivative represented by

where Ar represents an aryl group, and R represents an (a) an alkylgroup, (b) an alkyloxy group, (c) a dialkyl amine group with a hydrogenand carbon number of 1 to 10, (d) F, (e) Cl, (f) Br, (g) I, or (h) CN.9. A display unit comprising a plurality of organic light emittingdevices, each organic light emitting device being on a substrate andincluding a lamination structure that has: (a) a cathode, (b) aplurality of layers including an ordered arrangement of (i) an electroninjection layer, (ii) an electron transport layer, (iii) a lightemitting layer made of an organic material, (iv) a hole transport layer,and (v) a hole injection layer, and (c) an anode including a metal thinfilm with a top surface and a bottom surface, wherein, a resonatorstructure is configured to resonate light generated in the lightemitting layer between the cathode and the anode such that the light isemitted through the top surface of the anode and in a direction oppositeto that of the substrate, the cathode is reflective, the anode issemi-transparent to the light generated in the light emitting layer, theanode comprises a magnesium-silver alloy in which a ratio of Mg:Ag is10:1, the anode having a thickness that is less than a thickness of thecathode, the thickness of the anode being 10 nm, the anode is disposedabove the hole injection layer such that the bottom surface of the anodeis in contact with the hole injection layer and faces the substrate, theelectron injection layer is between the electron transport layer and thecathode such that the electron injection layer has one surface incontact with the electron transport layer and another surface in contactwith the cathode, the electron injection layer is a laminate structurethat includes a first film comprising a magnesium-silver alloy and asecond film comprising an alkali metal or an alkali earth metal, thecathode is between the electron injection layer and the substrate, athickness of the electron transport layer is greater than a thickness ofthe electron injection layer, the plurality of layers are formed suchthat the light emitting layer is closer in distance to the cathode thanthe anode in a thickness direction, and a light absorptance a of themetal thin film satisfies α=100−(R+T), where a is a light absorptancepercentage in a wavelength band from 400 nm to 800 nm of the metal thinfilm, R represents a reflectance percentage of the metal thin film to aside of the plurality of layers, and T represents a transmittancepercentage of the metal thin film.
 10. The display unit according toclaim 9, wherein the substrate is a driving substrate that includes atransistor.
 11. The display unit according to claim 9, wherein athickness of the hole injection layer is at least 4 nm.
 12. The displayunit according to claim 11, wherein the thickness of the hole injectionlayer is not greater than 8 nm.
 13. The display unit according to claim9, wherein the first film has a thickness of 2 nm.
 14. The display unitaccording to claim 9, wherein the hole transport layer comprisesbis[(N-napthyl)-N-phenyl]benzidine (α-NPD).
 15. The display unitaccording to claim 9, wherein the first film is thicker than the secondfilm.